This statute is not unsafe speed for conditions nor is it following too closely.
The "Inattention to Driving" statute has no equivalent RCW so the DOL is not able to enter them in their computer records. Thus, "Inattention" is an invisible ticket and a very desirable resolution in a majority of cases. This officer did your brother a favor and wrote him a ticket which won't appear on his record. However, the accident will appear on his record (and the associated insurance increase will happen), so the only reason to contest the ticket would be to avoid paying the $124 fine.
You can contest the ticket and hope that your brother made no incriminating statements to the officer and that no other witnesses show up. Accident cases are a headache in most cases as they're almost entirely worthless to prosecute.

